The present invention relates to a method of controlling a seatbelt retracting device having a mechanism for retracting a seatbelt with a motor.
A seatbelt retracting device mounted to a motor vehicle or the like has a function of winding an excess portion of a seatbelt after an occupant withdraws the seat belt and attaches a tongue to a buckle device. A conventional seatbelt retracting device is provided with a single return spring for performing such a function. Accordingly, when an occupant withdraws a seatbelt against an urging force of the return spring to fasten the seatbelt, and releases a hand after attaching the tongue to the buckle, the seatbelt retracting device winds an excess portion of the seatbelt with a force of the return spring so that the seatbelt fits the occupant.
As described above, the seatbelt retracting device has the function of winding an excess portion of the seatbelt so that the seatbelt fits the occupant. When the seatbelt is not used, the seatbelt retracting device winds the seatbelt until the seatbelt is completely stored in a storage unit. At the same time, when the seatbelt is used normally, the seatbelt retracting device needs to prevent an unnecessary pressure on the occupant. However, in the seatbelt retracting device having the single return spring, when an urging force of the spring is reduced to alleviate the pressure on the occupant, the urging force may not be enough to smoothly retract the seatbelt (for storing), thereby suffering operability and storability. In contrast, when the urging force is increased to provide a sufficient retracting force for the retraction, an unpleasant pressure may be applied to the occupant.
Further, in the conventional seatbelt retracting device provided with a single return spring, the return spring is wound as the seatbelt is withdrawn, thereby increasing the urging force as the withdrawn amount of the seatbelt increases.
In order to solve the problems described above, there has been a seatbelt retracting device, in which a motor or a combination of a motor and a return spring winds a seatbelt, as disclosed in Japanese Patent Publication (Kokai) No. 2001-225720. Such a seatbelt retracting device having a motor for retracting a seatbelt has been also disclosed in Japanese Patent Publications (Kokai) No. 11-301407 and No. 11-334533.
In general, a seatbelt retracting device with a motor is controlled to shut off power to the motor when a seatbelt is completely retracted. If the power to the motor is left on when the seatbelt is completely retracted, power source of a battery is wasted. Further, the motor may be overheated, thereby making it necessary to use a motor with high heat resistance. Accordingly, in the conventional control system, a current flowing to the motor is monitored. When the current exceeds a predetermined value, it is determined that the seatbelt is completely retracted, and the power to the motor is shut off.
In the conventional control system, it is determined that the seatbelt is completely retracted when a relatively large current is detected, so that it is possible to securely retract the seatbelt. However, in a case that a part of an occupant, e.g. an arm, is caught in the seatbelt during retraction, a retraction force of the motor tightens the part of the occupant, thereby imposing a pressure on the occupant. If the occupant tries to withdraw the seatbelt during the retraction, it is necessary to withdraw the seatbelt with a strong force against the retracting force of the motor.
The seatbelt retracting device may be deteriorated with time, and it is necessary to increase a torque for winding the seatbelt, or an output of the motor is lowered. In such a case, if it is set to determine that the seatbelt is completely retracted at a relatively small current, it may be determined that the seatbelt is completely retracted before the seatbelt is actually retracted completely, and the power to the motor is shut off, resulting in insufficient retraction.
In view of the problems described above, an object of the present invention is to provide a method of controlling a seatbelt retracting device with a motor in which it is possible to securely retract a seatbelt in a normal state. Further, it is possible to prevent a pressure on an occupant when a part of the occupant is caught in the seatbelt, and to withdrawn the seatbelt with a small force during retraction.
Further objects and advantages of the invention will be apparent from the following description of the invention.